1. Field of the Invention
The present invention relates to a heat development processor having a heat roller whose peripheral surface is heated to a predetermined temperature by a heat source so as to form a visible image on a heat-developable light-sensitive material with a latent image formed thereon, by effecting heat development while transporting the heat-developable light-sensitive material in close contact with a portion of the peripheral surface of the heat roller.
2. Description of the Related Art
As a means of heat treating a heat-developable light-sensitive material, a heat roller is generally used. Namely, as a heat-developable light-sensitive material with a latent image formed thereon is transported while being brought into close contact over a predetermined length with a peripheral surface of a heat roller heated to a predetermined temperature, the heat-developable light-sensitive material wound around the peripheral surface is heated, and an image is made visible on the heat-developable light-sensitive material.
As a heat-developable light-sensitive material, it is possible to use a material in which one of the following materials is provided on the surface of a base: one in which two components of a two-component-type heat-sensitive color-development medium are separated from each other by a microcapsule containing a photocurable composition placed therebetween (refer to Japanese Patent Application Laid-Open No. 89915/1977); one in which a layer containing a photopolymerizable composition and a vinyl monomer having an acidic group, an isolating layer, and a layer consisting of an electron donative colorless dye are laminated (refer to Japanese Patent Application Laid-Open No. 123838/1986); one which has a plurality of light-sensitive layers which develop different colors, each light-sensitive layer having a central wavelength (refer to Japanese Patent Application Laid-Open Nos. 224930/1989 and 19710/1990).
Since the heat roller heats the heat-developable light-sensitive material in direct contact therewith, the heat roller has higher thermal efficiency and a shorter processing time than other heating means (hot air, an infrared heater, etc.), and the apparatus becomes compact.
However, if the heat-developable light-sensitive material is subjected to heat treatment, water contained in the heat-developable light-sensitive material evaporates and is released in the form of steam. For this reason, steam is accumulated between the contact surface of the heat-developable light-sensitive material and the contact surface of the heat roller. The pressure of the steam can cause a portion of the heat-developable light-sensitive material, which must be kept in close contact with the heat roller, to float, so that its contact with the heat roller becomes insufficient, possibly resulting in uneven development. In addition, the floating of the portion of the heat-developable light-sensitive material causes a decline in the efficiency of heat transfer.
To overcome this problem, it is conceivable to adopt a means in which, before the heat-developable light-sensitive material is wound around the heat roller in close contact therewith, the water contained in the heat-developable light-sensitive material is removed in advance by preheating the heat-developable light-sensitive material such as by blowing hot air onto it or applying infrared rays onto it or the like.
With the above-described conventional means, however, it is necessary to provide a preheating zone for removing the water in advance, so that the processing time becomes long and the apparatus becomes large in size.
Meanwhile, to bring the heat-developable light-sensitive material into close contact with the heat roller over a predetermined length, such a heat development processor adopts a technique in which a plurality of backup rollers are arranged in face-to-face relation with the peripheral surface of the heat roller, and tension is applied to the heat-developable light-sensitive material by these backup rollers. In so doing, it is conceivable to weaken the nipping force of the backup roller located on the winding-start side so as to squeeze out bubbles which are released.
With such a technique, however, there are cases where bubbles remain, and the removal of steam cannot be effected reliably. In addition, the adjustment of the nipping force of the backup rollers is difficult.
On the other hand, to bring the heat-developable light-sensitive material (particularly its leading and trailing ends) into close contact with the peripheral surface of the heat roller over a predetermined length thereof as described above, it is effective to provide a guide plate (planar member) in face-to-face relation with the heat roller between the backup rollers or at other appropriate positions.
However, since such a guide plate is secured to the apparatus, the guide plate .comes into slidable contact with an emulsion surface of the heat-developable light-sensitive material which is transported in close contact with the heat roller. For this reason, as a result of an experiment it became evident that if the surface of the guide plate is made flat and smooth, the heat-developable light-sensitive material adheres to the guide plate, and the threading characteristic for threading the heat-developable light-sensitive material becomes deteriorated. In particular, the generation of steam described above promotes adherence.
In other words, this adherence hampers the smooth transportation of the heat-developable light-sensitive material with the rotation of the heat roller, and the amount of heat received from the heat roller becomes nonuniform at various portions of an image, possibly resulting in uneven development.
On the other hand, if the contact surface of the guide plate is made coarse to prevent the adherence of the heat-developable light-sensitive material, streaks may form on the image and the scoring of the emulsion surface will occur, deteriorating the quality of the finished image.